SUMMARY
In Neon Bionic, GTK3 applications used to automatically change their colour scheme to match the colour scheme when the colour scheme is changed, but as of Neon Focal this no longer occurs. None of the GTK3 applications, excluding the mini free space indicators in Nemo file manager's sidebar, get coloured at all by the colorreload-gtk-module when changing a colour scheme.

STEPS TO REPRODUCE
1. Apply a colour scheme
2. Open a GTK3 application
3. Apply another colour scheme

OBSERVED RESULT
The colour scheme isn't changed in that GTK3 application, or in fact any GTK3 applications.

EXPECTED RESULT
The colour scheme would also change immediately in other GTK3 applications.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: KDE neon User Edition 5.19.4 on Ubuntu 20.04
(available in About System)
KDE Plasma Version: 5.19.4
KDE Frameworks Version: 5.73.0
Qt Version: 5.14.2

ADDITIONAL INFORMATION
This worked just fine in Ubuntu 18.04 based Neon.